o Hydrology:

o Erosion

Denudation by wind, water, or ice, which dislodges, dissolves, or removes surface material.
o Water dislodges, dissolves, or removes surface material in the erosion process.
o Thus a stream is a mixture of water and solids; the solids are carried in suspension, by mechanical transport, and in dissolved solution.

o Alluvium

o Base level:

is a level below which a stream cannot erode its valley. In general, the ultimate base level is sea level, the average level between high and low tides.
o Base level: A hypothetical level below which a stream cannot erode its valley, and thus the lowest operative level for denudation processes; in an absolute sense, it is represented by sea level, extending under the landscape.
o • base level (Powell; USGS): the level below which a stream cannot erode its valley
o • imaginary surface extending inland from sea-level (lowest level of denudation processes)
o • local base-level: river, lake, resistant strata (lower limit of local streams)

o Sheetflow

o Continental divides:

A ridge or elevated area that separates drainage on a continental scale; specifically, that ridge in North America that separates drainage to the Pacific on the west side from drainage to the Atlantic and Gulf on the east side and to Hudson Bay and the Artic Ocean in the north.

o Internal drainage

In regions where rivers do not flow into the ocean, the outflow is through evaporation or subsurface gravitational flow. Portions of Africa, Asia, Australia, and the western United States have such drainage.

o Drainage density:

: A measure of the overall operational efficiency of a drainage basin, determined by the ratio of combined channel lengths to the unit area. Determined by dividing the total length of all stream channels in the basin by the area of the basin.

o Drainage pattern:

A distinctive geometric arrangement of streams in a region, determined by slope, differing rock resistance to weathering and erosion, climatic and hydrologic variability, and structure controls of the landscape.

Dissolved load

suspended load

fine particle held in suspension in a stream. The finest particles are not deposited until the stream velocity nears zero. Consists of fine-grained, clastic particles (bits and rock).
o Turbulence in the water, with random upward motion, is an important mechanical factor in holding a load of sediment in suspension.

bed load

refers to coarse materials that are dragged, rolled, or pushed along the bed of a stream by traction or by the rolling and bouncing motion of saltation; involves particles too large to remain in suspension.

saltation

Aggradation

The general building of land surface because of deposition of material; opposite of degradation. When the sediment load of a stream exceeds the stream's capacity to carry it, the stream channel becomes filled through this process.

braided stream

A stream that becomes a maze of interconnected channels because it is laced with excess sediment. Braiding often occurs with a reduction of discharge that reduces a stream's transporting ability or with an increase in sediment load.
o • laminar - streamlined, smooth flow with suspended particles move in parallel (deep and smooth channels)
o • turbulent - mixing flow, with increased transport (shallow streams, rough channel). Flow becomes turbulent is shallow stream or where channel is rough

Undercut bank

Point bar

In a stream the inner portion of a meander, where sediment fill is redeposited because the inner portion of the a meander experiences the slowest velocity and this receives sediment fill, forming a point bar.

Oxbow lake

A lake that was formerly part of the channel of a meandering stream; isolated when a stream eroded its outer bank forming a cutoff through the neck of the looping meander. In Australia known as the billabong. (Easier to understand: When the former meander becomes isolated from the rest of the river; the resulting oxbow lake may gradually fill with organic debris and silt or may again become part of the river when it floods.)
o Mississippi River is many miles shorter today than it was in 1830s because of artificial cutoffs that were dredged across meander necks to improve navigation and safety.
o Oxbow lake: erodes outer bank (neck)=neck narrows=erodes, forms cutoff = isolated from channel =stream becomes straighter

o Stream Gradient

A graded stream is one in which over a period of years, slope is delicately adjusted to provide, with available discharge and with prevailing characteristics, just the velocity required for transportation of the load supplied from the drainage basin. By J.H Mackin
o • stream gradient: elevation decline over distance from headwaters to mouth; concave shape
o • graded stream - balance (dynamic equilibrium) btw erosion, transportation, and deposition
o • stream gradients may be affected by tectonic uplift of the landscape which changes the base level balance (gradient) =further down-cutting=rejuvenation

Gradient

The drop in elevation from a stream's headwaters to its mouth, ideally forming a concave. Every stream runs downhill under the pull of gravity. In the course of this process, each stream develops its own gradient: which is the rate of elevation decline from its headwaters to its mouth.

Graded stream

o Nickpoint

The point at which the longitudinal profile of a stream is abruptly broken by a change in gradient; for example a waterfall, rapids, or cascade.
o Conversion of potential energy in the water at the lip of the falls to concentrated kinetic energy at the base works to eliminate the nickpoint interruption and smooth out the gradient.
o • nickpoints - abrupt change in gradient (e.g. waterfall) • potential energy kinetic energy: eliminate nickpoint (geology)
o • Waterfall - water in freefall =erosion at base =undercuts, collapse and shift upstream
o • Waterfall = series of rapids
o • Niagara Falls - 11km retreat from the Niagara Escarpment in 12,000

Floodplain

o Natural levees

A long low ridge that forms on both sides of a stream in a developed floodplain; they are depositional products of river flooding.
o When floodwater rises the river over flows its banks, loses stream competence and capacity as it spreads out, and drops a portion of its sediment load to form the levees. Larger sand sizes particles drop out first, forming the principal component of the levees, with finer silts and clays deposited farther from the river.

Backswam

Alluvial terraces

: Level areas that appear as topographic steps above a stream, created by the stream as it scours with renewed down cutting into its floodplain; composed of unconsolidated alluvium.
o Represents what originally was a depositional feature (a floodplain) that subsequently has been eroded by the rejuvenated (tectonic uplift) stream.